The invention relates to a novel readily soluble crystal modification (hereafter referred to as xe2x80x9cthe first crystal modificationxe2x80x9d) of the compound of formula I 
in which the transmission X-ray diffraction pattern obtained with a focusing Debye-Scherrer beam and Cuxe2x80x94Kxcex11-radiation, has lines at the following diffraction angles 2xcex8:
Lines of strong intensity: 10.65; 14.20; 14.80; 16.10; 21.70; 23.15; 24.40; 24.85; 25.50:; 25.85; 26.90; and 29.85 degrees,
Lines of medium intensity: 7.40; 9.80; 13.10; 15.45; 16.80; 20.70; 21.45; 22.80; 23.85; 27.25; and 28.95 degrees,